chore: updating to ethereumjs-util@6

[martinheidegger]

Updating ethereumjs-util to its latest version @ethereumjs/util v7 would require more effort. This PR limits the update to v6 which only required to rename sha3 with 256bit to keccak. In the tests the message had to also match the format in order to pass the new error sensibly triggered since 6.2.0.

[mcmire]

This is a nitpick, feel free to take or leave, but it's probably more idiomatic to say this, yeah?

Suggested change

	const keccak256 = require('ethereumjs-util').keccak256;
	const { keccak256 } = require('ethereumjs-util')

[mcmire]

This looks good — do you mind rebasing this? Hopefully it'll kick GH Actions to do its magic.

[mcmire]

Thank you for this pull request, but we are actively phasing out this package in favor of json-rpc-engine and its related packages, so I'm going to close this. As for the changes here, we no longer have an Etherscan-specific middleware, and one of the main packages in our ecosystem that accesses ethereumjs-util now is @metamask/eth-sig-util. We have since upgraded to using @ethereumjs/util there.